1. Field of the Invention
One or more embodiments of the present invention relate to a battery pack, and more particularly, to a battery pack formed by coupling a cover case and a bare cell.
2. Description of the Related Art
Recently, portable electric/electronic devices are being made compact and light, for example compact and light cellular phones, notebook computers, camcorders, etc., are being actively developed and produced. Accordingly, portable electric/electronic devices include battery packs so as to be operated even in places where additional power sources are not available. Recently, battery packs have employed economical secondary batteries which are capable of charging and discharging. Representative secondary batteries include a nickel (Ni)-cadmium (Cd) battery, a Ni-MH battery, a lithium (Li) battery, a Li-ion secondary battery, etc. In particular, operation voltage of the lithium ion secondary battery is about three times higher than that of the Ni—Cd battery or the Ni-MH battery, which are usually used as a power source for portable electronic devices. Also, the Li-ion secondary battery is widely used in view of high energy density per unit weight. Secondary batteries generally use lithium-based oxides as positive electrode active materials and carbon-based materials as negative electrode active materials. In general, a secondary battery may be a liquid electrolyte battery or a polymer electrolyte battery according to the type of electrolyte in the secondary battery. In this instance, a Li battery using a liquid electrolyte is referred to as a Li-ion battery, and a Li battery using a polymer electrolyte is referred to as a lithium polymer battery. A secondary battery is formed of a bare cell formed by sealing a can accommodating an electrode assembly and an electrolyte, and a protection circuit substrate electrically connected to the bare cell. The bare cell charges/discharges electricity via a chemical reaction. The protection circuit substrate controls charging/discharging of the bare cell and prevents overcharging/overdischarging of the bare cell to protect the bare cell. When the bare cell and the protection circuit are connected to form the secondary battery, electrical resistance therebetween should be reduced in order to improve charging/discharging efficiency. In more detail, if the electrical resistance between the bare cell and the protection circuit module is high, the charging/discharging efficiency of the bare cell is reduced.
Meanwhile, the secondary battery may be put through a reliability test for determining whether the secondary battery is stable enough to withstand impact caused when mounting the secondary battery in an electronic product, after being formed in a pack by integrally connecting the bare cell and the protection circuit substrate. If there is an external impact, the electrical resistance between the bare cell and the protection circuit substrate could conceivable be increased. The electrical resistance increases as contact resistance increases in a part where the bare cell and the protection circuit substrate are connected.